Process of extruding an aqueous dispersion containing viscose and an acrylonitrile polymer



United States Patent 3,235,642 PROCESS OF EXTRUDING AN AQUEOUS DIS-PERSION CONTAINING VISCOSE AND AN ACRYLONITRILE POLYMER Richard N.Blomberg, Wilmington, Del., assignor to E. I. du Pout de Nemours &Company, Wilmington, Del., a corporation of Delaware No Drawing. FiledJuly 24, 1962, Ser. No. 212,131 4 Claims. (Cl. 264-182) V This inventionrelates to compositions of acrylonitrile polymers and to shaping of theminto articles, such as filaments or films, by extrusion. Thisapplication is a continuation-in-part of application Serial No. 512,591filed June 1, 1955, now US. Patent 3,087,903.

Conventional processes of extruding acrylonitrile polymers arecomplicated by necessity of polymer purification, solution, andhigh-temperature treatment. The relatively ditficult solubility ofacrylonitrile polymers containing high percentages of acrylonitrile haslimited development of methods for preparing shaped articles from them.

An object of the present invention is formation of novel dispersions ofacrylonitrile polymers, A further object is production ofself-supporting articles of novel composition from dispersions ofacrylonitrile polymers. Other objects, together with means and methodsfor accomplishing the various objects, will be apparent from thefollowing description.

In general, the objects of the present invention are accomplishedthrough production and use of disperse compositions containing bothviscose and acrylonitrile polymers. The invention comprehendsparticularly combination of a stable aqueous dispersion of anacrylonitrile polymer in which up to about one-fourth of the totalweight of the dispersion is acrylonitrile polymer with a viscosesolution containing up to about seven and onehalf percent of freecaustic by weight (calculated as sodium hydroxide). In the resultantcomposition the viscose apparently serves as a sort of matrix for thedispersed particles of acrylonitrile polymer, thus preserving theintegrity of the product even upon extrusion; greater content ofacrylonitrile polymer is conducive to coagulation, and higherconcentration of free caustic fosters occurrence of agglomerates, eitherof which phenomena is detrimental to successful formation of extrudedarticles.

As used here, the term viscose has its customary meaning. It signifiesthe product of reacting cellulose with caustic (i.e., aqueousalkali-metal hydroxide), then reacting the resulting alkali cellulosewith carbon di sulfide, and finally dissolving the cellulose xanthate soobtained in an excess of caustic solution. The viscose should containapproximately 4% to 12% cellulose by weight, with the optimum being inthe middle of this recommended range; also the degree of xanthatesubstitution should be in the range of 0.3 to 1.0. Conventional viscosesare in the lower part of the range for each of these variables. Thequantity degree of xanthate substitution is based on the number ofpositions available on the glucose ring for substitution. As there arethree of these (hydroxyl groups) in each glucose unit, the maximumdegree of substitution has a value of 3.0; however, as suggested, theaverage number of xanthated hydroxyl groups per molecule of celluloseused here should be from about 10% to a little over 30% of the maximum.

An acrylonitrile polymer here is a substance of high molecular weightcontaining repeating -CH1CH units throughout the molecular structure,thus including not only the homopolymer of acrylonitrile but alsocopolymers of acrylonitrile with other copolymerizable monomers,particularly ethylenically unsaturated monomers, so long as thepolymerized acrylonitrile units predominate in weight and number in thecopolymer, It also comprehends compositions containing, in addition tothe polymer proper, small quantities (e.g., a few percent by weight) ofother materials, whether monomeric or polymeric or whether usuallyconsidered beneficial or detrimental to convention-a1 use of thepolymer.

Acrylonitrile polymer dispersions obtained by conventional emulsionpolymerization techniques can be used directly for mixing with viscose,if the concentration of polymer is below about 25%. The acrylonitrilepolymer particles will obviously be smaller than the spinneret orificesemployed and preferably will be, on the average, below ten microns.Improved results are obtained if the polymer dispersions are stabilizedbefore combination with the viscose. For example, less subsequentagglomeration is observed if the polymer dispersion is deionized bypassing through a cationic-exchange resin prior to mixing with theviscose. Still further improvement is obtained if sufficient ammoniumhydroxide is added to the deionized dispersion to raise the pH toapproximately9-l0. The molecular weight ofthe acrylonitrile polymershould be high enough to endow fibers or films made therefrom withdesired physical characteristics of toughness, high softeningtemperature, and relative insolubility in ordinary solvents. Polymers oflimited viscosity number (International Union of Pure and AppliedChemistry, J. Poly Sci., 8, p. 257, 1952) at least 2.0 are preferred.One of the primary advantages of this invention is the practicability ofusing in dispersed form polymers of such high molecular weight thatconventional methods of shaping articles from them are limited severelyby accompanying high viscosity.

After mixing, the resultant composition is extruded through a suitableorifice, slot, or the like to form a selfsupporting article, Appropriatetreatment of the extruded article coalesces the polymer particles into acontinuous structure, which has greatly increased tensile strength aftera suitable drawing. This treatment may regenerate cellulose from theviscose or not, as desired, the shaped article retaining a cellulosiccomponent distributed throughout the resulting structure.

The practice of this invention is exemplified below in some detail, thetext of the example, including for con venience an account ofpreparation of a suitable dispersion of acrylonitrile polymer andstabilization of it by addition of an anionic dispersing agent andsubsequent deionization, as is generally preferable for improvedcontinuity of extrusion through fine orifices. In the illustrationswhich follow, all parts are by weight unless otherwise indicated.

An aqueous dispersion of polyacrylonitrile is prepared in a stainlesssteel kettle from 0.05 part potassium persulfate, 1.0 part sodium Lorolsulfate (comprises a mixture of straight chain alkyl sulfon-atespredominantly lauryl and myristyl sulfates, which is a well-knownanionic dispersing agent, 60 parts of water, and 45 parts ofacrylonitrile, and the free space of the kettle is flushed with nitrogengas and then sealed. After relatively mild agitation of the contents for16 to 17 hours at 40 C., the resulting polymer dispersion contains 40%solid ma terials as is determined by evaporation of a portion. Thedispersion has a uniform milky appearance and a pH of about 6.5.Sufficient Amberlite IR-l20 (H), which is a well-known water-insolublephenol-formaldehyde type of cationic exchange resin, is added todisplace one-fifth the volume of dispersion. After stirring for about 5minutes, the resin is removed by coarse filtration and water is added toreduce the non-aqueous content of the dispersion to about 20% by weight.The instantaneous pH, which is slightly under 2 at this stage, is raisedto about 10 by the addition of one part of 28% .ammoniurn hydroxide toeach wenty parts of .the dispersion. p 1- A viscose solution containing2.4% excess caustic (as sodiurnhydroxide) and about 5% cellulose byweight with a degree of substitution of 0.62 is stirred rapidly into the20 .dispersion Qne volume of the viscose ,is usedfor eachthree volumesof the dispersion. The acrylonitrile polymer now constitutes about 15%of the total weight .of the dispersion, the cellulose concentration isnow about 1.25% and thefree caustic present istherebyaeduced to about-0.6%. The resulting composition is deacr-ated at a pressure equivalentto about 20 mm. of mercury for 20-30 minutes. I This spin mix isextruded at a pressure of -15 pounds per square inch through a spinneretwith five 0.008 inch holes at a rate of 30 yards per minute intoatypical cellulose regeneration bath maintained at 25 C. and containing9.4% sulfuric acid (1.84 specific gravity), 6.8% zinc sulfatehexahydrate, and 15.5% sodiumsulfate decahydrate. After 5 seconds inthisbath, theresulting filaments are exposed for 3-4 seconds to a bathcontaining 60% aqueous calcium thiocyanate heated to 110 C. They arewashed with water and drawn at 140 C. to provide filaments with atenacity of from 3-5 gramsper denier and an elongation of 10-15%. Thefilaments have a density of approximately 1.2 grams per cc. and containapproximately 5.9% of cellulose or its derivatives.

In an attempt to follow the procedure of the above example using aviscose which has a degree of substitution of 0.4 and an initialacrylonitrile dispersion containing approximately 40% polyacrylonitrile,complete coagulation occurred. Reducing the concentration ofacrylon-itrilepolymer to about 30% did not show any appreciableimprovement. A spin mix prepared in a manner identical to thatexemplified above, except that it, contained more excess caustic,wasless smooth, a few outsize agglomerates appearing clearly at amagnification of 500 diameters when the viscose used contained 5% excesscaustic, and many agglomerates running several hundred times thediameter of the norm-a1 dispersed particles being visible when 7.5%excess caustic was present. When present in an appreciable number -say20%, agglomerates of the order of 10 times thenor-mal diameter aresufficiently outsized to raise the extrusion pressure appreciably, andanother tenfold increase in either number or size of agglomerates,renders themixextrudable (at the indicated fineness only withdiificulty. A further increase also gives rise to discontinuity ofspinning because of clogging of the 'spinneret orifice or breakageotherwise caused in the extruded filament. V I I V eplacing the viscosedescribed above, which has a 0 .4 degree of substitution, with a viscoseof 0.5 degreeof xanth-ate substitution gave satisfactory results.However, the tendency toward mutual coagulation is higher at the higherconcentrations and stabilization of the polyacrylonitrile dispersion ispracticallyv essential. For example, when the deionizedpolyacrylonitrile dispersion was not stabilized with ammonia, theaddition of theviscose with the higher xanthate concentration led toappreciable agglomeration. .Use of viscoses containing less thanabout;0.3 degreeof'xanthate produced weaker extruded filaments; thisstrength reduction is undesirable because the filament normally (i.e.,in a continuous process) undergoes some forwarding tensionbeforecoalescence of the acrylonitrile polymer particlesitakes place toform/the ultimate desired structure. Viscose containing cellulosex-anthate with a degree of substitution of about 0.3 is somewhat moresusceptible to agglomeration than the one described in the example. Onceagain, this eifect is more noticeable when the ammonia stabilization ofthe polyacrylonitrile dispersion is omitted.

At the lower caustic concentrations an accompanying higher degree ofxanthation of the cellulose is desirable to increase the stability ofthe viscose solution. For example, viscose having a degree ofsubstitution of. about 0.3"re quires at least about 2.5% excess causticto prevent gelling. This particular composition represents, aboutthelower limit ofxanthate substitution and free caustic recommendedfor useaccording to the present invention.

While the regenerating bath maybe omitted, the coalescence step isthen-conductive to the torm'ation of residual sulfur, which isundesirable for textile purposes. Presence of several percent ofcellulose finely divided in the final article makes it lesshydrophob-icthan customary acrylonitrjle polymers lacking it, with consequentbeneficial efiect, especially in textile uses. Other hydrotropic saltsolutions, e.g., zinc chloride, may replace calcium thiocyanate in thecoalescing bath, or organic solvents or plasticizers for theacrylonitrile polymer maybe used instead. Although not essential, bathtemperatures above room temperature are generally used to carry out theprocess .in a reasonable length of time; the temperature should remainsomewhat below {the boiling point of the bath to avoid turbulence, whichis undesirable duringllle formationof the shaped article.

The product may bedrawn before or after drying, as for increasing itstenacityin the well-known mannen, Filaments and films formed accordingtothis invention can be dye or printed more readily than the avail-ableacrylcit le Po yme s. po s b yibec usec the el los -content or thesomewhatmore open structureso obtained. The advantages of producingfilaments, films,.ribbons, and the like with the aid of, the presentteachings willbe apparent to those skilled in the art,of shapingpolymeric articles by extrusion. v v

What is claimed is: I

1. The process of extrudingan, aqueous dispersion containing viscoseandapredominantly acrylonitrilepolyrner containing about 1.25% cellulosexanthate calculated as cellulose, about 0. 6% free caustic, and saidviscose having a xanthate substitution of about 0.,62 iand said polymcr.constituting about 15% of. the total :weight of the dispersion into abath effective toregeneratc cellulose from the viscose to formaself-supporting article containing the finely dividedacrylonitrilepolymer.

2. Process of treating theproduct of claiml with a bath efiective tocoalesce the finely divided arcylonitrile polymer.

V 3. The process of claim 2 inwhich the .activeingredient of thecoalescing bath. is calcium thiocyanate.

,4. The process of extruding through a sp-inneret, a mixture of aboutl'volumeof a viscosesolution and 3 vol: umes ofan aqueous dispersionofia predominantly acrylonitrilepolymer, the viscose solution containing2.4% .excess caustic and about 5% by .weight ,of, cellulose having adegree of xanthate substitution of 0.62 and the polymer dispersioncontaining about 20% by weight of solids; treatingtheextrudate with .abath effective to. regenerate cellulose from the. added viscose, andcoalescing the finely divided acrylonitrile polymer. 1 f

, I H Referencie s Cited by the Examiner I I UNIVTEDSTAIES' PATENTS2,726,220 12/1955; Ogden1' '26017 2,796,65 '16/1957] 1 2,858,185 10/1958JOSEPH L. SCHOFE'R, Primary Exa' m iner.

JAMES A. SEIDLECK, Examiner.

1. THE PROCESS OF EXTRUDING AN AQUEOUS DISPERSION CONTAINING VISCOSE AND A PREDOMINANTLY ACRYLONITRILE POLYMER CONTAINNG ABOUT 1.25$ CELLULOSE XANTHATE CALCULATED AS CELLLOSE, ABOUT 0.6% FREE CAUSTIC, AND SAID VISCOSE HAVING A XANTHATE SUBSTITUTION OF ABOUT 0.62 AND SAID POLYMER CONSTITUTION ABOUT 15% OF THE TOTAL WEIGHT OF THE DISPERSION INTO A BATH EFECTIVE TO REGENERATE CELLULOSE FROM THE BISCOSE TO FORM A SELF-SUPPORTING ARTICLE CONTAINING THE FINELY DIVIDED ACRYLONITRILE POLYMER. 